There has been proposed a memory device system that includes a first memory and a second memory (a duplicated memory) formed so as to store the same data, and a comparator that compares the data stored in the first memory with the data stored in the second memory to determine whether the data is normal or abnormal (for example, Patent Literature 1). Specifically, in such a memory device system, the data stored in each of the first memory and the second memory is once stored into each of a first register and a second register, and the comparator reads the data stored in the first memory and the data stored in the second memory for comparison. Incidentally, in such a memory device system, all pieces of the data stored in each of the first memory and the second memory are stored into each of the first register and the second register at a time.